In magnetic recording technology it is constantly desired to improve the areal density at which information can be recorded and reliably read. This desire has lead a trend toward shrinking track widths and greater bit density along a magnetic recording track.
One of the important parameters which determine the performance of a magnetic head is the gap length. The gap length is defined by the separation of two magnetic pole pieces at the transducing gap. The separation of the pole pieces is usually established by a gap forming layer of non-magnetic material. A second important parameter affecting performance of a magnetic head is the width of the pole tips. This dimension can be less than ten microns and must be closely controlled in order to achieve optimum performance. A third important parameter which determines the performance of a magnetic head is the throat-.height. This parameter is measured from the pole tip face to a so-called zero throat point which is the point at which the upper and lower magnetic pole pieces begin to diverge in order to enclose the coil.
Magnetic heads are currently made by using thin film photolithographic technology. This technology permits the fabrication of heads having much smaller transducing gaps than the arrangements priorly used. U.S. Pat. Nos. 4,190,872, 4,589,042 and 4,652,954 disclose magnetic heads fabricated with the use of thin film photolithographic technology. This technique successfully deposits a number of films on a substrate during head fabrication. The magnetic structure of the heads comprises a pair of magnetic films separated by layers of insulating films and by one or more layers having turns of conductive material. These turns comprise the windings of the head and they perform the reading and writing functions of the head. The pair of magnetic films comprises a lower film and an upper film which together comprise the magnetic head structure. The magnetic structure includes a main body portion and a pole piece portion.
The trend toward increased areal densities requires narrower pole tips and shorter throat heights. It has heretofore been difficult to fabricate devices that consistently meet these requirements. One important reason for this is that the upper magnetic film layer is typically photographically defined and deposited after the layers comprising the coil structure have been deposited. This coil structure is relatively thick and is approximately three to five times the thickness of the pole pieces. Since the upper pole piece layer must cover the relatively thick coil structure that has already been built up, it is difficult to deposit a layer of photo defining material that is thin in the area of the pole tips and, at the same time, covers the coil structure with optimum depth to provide precise definition to both areas. Because of this difficulty, a plurality of units produced during a production run of these devices will yield relatively few heads having the required narrow pole tips and short throat heights. The remainder of the production run will comprise devices that do not meet these requirements.
U.S. Pat. No. 4,190,872 attempts to solve this problem by depositing the layer comprising the upper pole piece in two stages using an appropriate mask for each stage so that the thickness of the upper layer in the back region is greater than in the pole tip region. See column 2, lines 63 through 65 of this patent. U.S. Pat. No. 4,589,042 also fabricates the upper magnetic layer in two separate steps. A pole piece area 24 of the upper layer is first fabricated followed by a fabrication of the back region portion of the upper layer. See columns 3 and 4 of this patent. Although the fabrication of the upper layer in two separate steps is an improvement over the prior art arrangements which deposit the upper layer in a single step, the upper pole tips produced by the methods of these patents are not consistently of the ideal dimensions since the upper pole tip layer is fabricated near the end of the process after the insulating layers and the layers comprising the coil structure are deposited.
It may be seen from above, that it is a problem to produce thin film heads by photolithographic techniques whereby the heads have narrow pole tips and the required width tolerances.